The interests and proposed course of the Biologic Structure Section is to characterize the role of the macrophage in antigen recognition by T lymphocytes in the expression and initiation of cell mediated immunity in man and experimental animals. More specifically, we are interested in exploring the role of the major histocompatibility complex in the genetic regulation of cell-cell interactions required for expression of cell mediated and humoral immunity. The Biologic Structure Section is also actively characterizing the physical state, localization, and fate of macrophage associated antigen. Additional studies of genetics of immune responsiveness to insulin in man will be assessed and compared to mouse and guinea pig. Determinant selection by macrophages functionally describes Ir gene control of antigen recognition by T lymphocytes in experimental animals. A understanding of the operation of a similar mechanism in man has implications in the pathophysiology of insulin allergy in diabetics.